About 10-14 days after the eggs are laid by the females, the adult flies emerge from their pupal cases.
In this lab, we performed a dihybrid cross for dumpy wing/normal eye color and normal wing/sepia eye color. In a dihybrid cross, two different mutants are crossed to each other and a sibling cross is performed with the progeny from the F1 generation. The dihybrid cross is performed to determine if two genes assort independently or if they are genetically linked. If the two genes assort independently, the expected phenotypic ratio is 9:3:3:1. If the two genes are on the same chromosome and linked, there will be fewer recombinants that have a phenotype different from either parent in the P generation. Since dumpy and sepia are both recessive traits, the F1 generation will be phenotypically wild-type.
The dependent variable is the number of each class of flies in the F2 generation (wild-type, dumpy, sepia, and dumpy/sepia). The controlled variables are the genotypes of the P1 and F1 generations. The P1 generation will be either red eyed, dumpy or sepia, normal wing. The F1 generation will all be heterozygous for both mutations. This is verified by making sure that the F1 flies used for the cross all have the wild-type phenotype for both wings and eyes.
Flies were sorted by genital morphology and the presence/absence of sex combs under a dissecting microscope following anesthetization with FlyNap. Flies were cultured and allowed to develop in vials with water added to dry media and supplemental yeast. Progeny from each cross were allowed to develop in the vials and emerging adults were collected. The P and F1 generations were sorted and 10 males and 10 females were placed in new culture vials with food to set up both crosses. The F2 progeny were counted by phenotype and the data was recorded. The phenotypes were scored as either dumpy or normal wings and red or sepia eyes. Χ2 statistical analysis